Flipping Quantum Coins

Poor Alice and Bob; they had been together so long, but now they’re breaking up. With no trust and a lot of miles between them, how can they decide who gets what? A coin flip would seem fair but not when both people are unable to view the flipped coin at the same time. So what they decide to do is Bob flips his coin and locks the results in a safe, before sending it to Alice. Alice then sends the result of her coin flip to Bob, who replies with the key to the safe. Now both people can see the results of both coin flips and neither could have cheated. This scenario is an analogy for a possible method of secure quantum communication.

Older methods of protecting quantum communication had been susceptible to cheaters, but not this. If Alice were to crack the safe open before sending her result to Bob, to guarantee her winning, the observation would be observable by Bob, due to quantum mechanics. So long as what is in the safe is entangled with something Bob still has, Alice observing it would trigger a change in what Bob can observe.

Researchers at the University of Calgary and at the SAIT Polytechnic (not named Alice and Bob) successfully demonstrated this technique across the 5 Km distance between them. Unfortunately, the flipping of quantum coins that far apart is not perfect, so cheating is still possible. However, cheating would not guarantee success and still presents the risk of getting caught, so the method is still relatively secure.

Don’t worry; I’m sure Alice and Bob will get back together before too long. There are still a lot of quantum mechanical phenomena to explain.